docs: def queue_emission(self, msg):
          """
          queue an emission of a message for all output plugins
          """
          if not msg:
              return
          for _emitter in self._emit:
              if not hasattr(_emitter, 'emit'):
                  continue
              def emit(emitter=_emitter):
                  self.log.debug("emit to {}".format(emitter.name))
                  emitter.emit(msg)
              self.log.debug("queue emission to {} ({})".format(
                             _emitter.name, self._emit_queue.qsize()))
              self._emit_queue.put(emit)